I have a 7 month old iPhone 15 Pro running iOS 17.4.1. Not a Pro Max. I set an alarm last night for this morning. I woke up early and and reached for my phone on the magnetic charger. I tapped on the screen to check the time. Nothing. The black screen of death. I tried the normal start by pressing and holding the side button. Nothing. I thought the phone had not charged overnight, even though it had over 70% charge when I went to bed. I plugged it into an Apple 20 watt charger, waited a few minutes to see if it would start charging. Nothing. So I did an internet search and found this group discussion. I tried the suggestion of quickly pressing the volume up, then volume down, followed by the normal side button start. Nothing.
I decided to try calling my phone from my iPad Pro. I used my Google Voice app and WiFi calling. Success. My iPhone display lit up with the Google Voice app showing that I was getting a call. I answered the call, said a couple of words to make sure it was working.
I hung up and my normal background home page appeared - folders and wallpaper.
Not sure what the problem is, hopefully Apple fixes it soon. I normally keep my previous iPhone and iPad in case my new ones have problems. I waited longer than normal before upgrading to my current iPhone and iPad. My older ones don’t support iOS 17.x.x. I won’t be waiting as long before I upgrade again. Fortunately, I had a new iPad Pro.
Hopefully this helps in case pressing all the buttons to force a restart fails.